Maybe try Colorado Model Structures...They're a large scale building manufacturer but they have a blue metal building that may work. The Kenrow Plastics's building is rather small in 1:29 scale as would only measure like 20' x 40' x 12' tall...a big garage really.
The owner is great to work with as far as doors and such.
Scroll down a bit... http://www.coloradomodel.com/default1.htm
